Metal aluminum is lightweight and used for materials for aircrafts, or the like. For example, when metal aluminum is used as a body of an aircraft, it is necessary to form a through hole for fastening a rivet. For use in machining such a through hole, for example, Patent Document 1 discloses a drill capable of machining an inlet of the through hole into a tapered surface by disposing a second cutting edge on a rear side of a drilling portion.